With the end of the last Ice Age, not only did glaciers and ice sheets melt away. One of the most impressive animal communities in Earth’s history also vanished: mammoths, woolly rhinoceroses, wild horses, and bison retreated from the northern regions of Eurasia and North America, forever. What remained was a question that has preoccupied paleontology for decades: Was humanity the decisive hunter, or did climate seal the fate of the Ice Age giants?
New analyses now provide a more nuanced picture. A research team led by evolutionary biologist Beth Shapiro of the University of California evaluated hundreds of bone finds from northern Alaska, from the so-called North Slope—an area that once marked the eastern edge of the mammoth steppe. The remains, up to 40,000 years old, come from classic representatives of Ice Age megafauna: mammoths, bison, horses, and musk oxen.
Comparing these age data with climate models supports a scenario first proposed in the 1990s by biologist R. Dale Guthrie: populations of large herbivores repeatedly went through extreme cycles of boom and collapse. The cause was not a single factor, but the interaction of climate, vegetation, and geography.
During cold periods, the mammoth steppe dominated—a dry, cold mosaic of grasses and herbaceous plants growing on mineral-rich loess soils. This landscape offered stable, though by no means abundant, living conditions. Only during irregular warm phases did the picture change fundamentally: the climate became wetter, soils more fertile, and plant growth exploded. For a few centuries, large herbivores encountered almost ideal conditions, and their populations grew rapidly.
But the boom carried the seeds of collapse within it. As moisture increased, soils became waterlogged and peat formed. Groundwater levels rose, mineral-rich dust from glacial regions no longer arrived, and soils became acidic. Nutrient-rich steppe plants disappeared, replaced by hardy species of little value to large animals. As a result, the previously exploding populations declined dramatically.
These collapses left genetic bottlenecks, and in some regions species even went locally extinct. Yet as long as cold periods returned, the mammoth steppe was never permanently lost. Herbivores migrated back in, populations recovered. Over tens of thousands of years, this rhythm of flourishing and collapse repeated itself.
Only with the onset of the Holocene did the situation fundamentally change. The current warm period lasted longer than all previous ones. Peatlands became permanently established, and the mammoth steppe never returned. At the same time, rising sea levels fragmented once continuous habitats. Migration routes were severed, populations became isolated and too small to persist in the long term.
Thus mammoths and their companions did not die out suddenly, but gradually, bogged down by changing ecosystems, scattered by rising seas. The last mammoths survived until about 3,700 years ago on Wrangel Island. But even there, their fate had long been sealed: cut off from the mainland, their retreat into a shrinking world was complete.
Rosamaria Kubny, PolarJournal